The present invention relates to a frequency marker generator and more particularly to a system for providing frequency marker pulses over a wide band of frequencies.
Various prior art devices have been used to provide frequency marker pulses. In such devices, the frequency marker pulses are provided by inductively or capacitively inserting fixed known frequency signals or mixing the signals having known frequencies with the high frequency sweeps to produce heterodyne beats. These methods are typically used for providing frequency marker pulses corresponding to high frequencies over band widths wherein the ratio of the highest frequency in the band width to the lowest frequency in the band width is in the order of 2 or 3 to 1.
These techniques however provide frequency marker pulses having numerous harmonic beats having frequencies which are multiples of the fundamental frequency of the frequency marker pulse. Thus, the prior art devices cannot be used for providing frequency marker pulses wherein the band width includes frequencies which are both the fundamental and harmonic frequencies of any of the frequency marker pulses. Thus, the prior art devices are not usable to provide frequency marker pulses to test systems wherein the ratio of the highest frequency in the band width to the lowest frequency in the band width is substantially higher than 3.
High fidelity amplifier systems operate in the audio spectrum of frequencies with the band width having frequencies between approximately 20 hertz and 20 kilohertz thereby having a ratio of the highest frequency in the band width to the lowest frequency in the band width of approximately 1000. Therefore prior art marker pulse devices would provide many harmonic or beat pulses in the audio band width or any other band width of interest. It has become necessary to test audio equipment such as tape recorders and cassette and cartridge devices for amplitude response at predetermined frequencies and such prior art devices cannot provide any accurate testing in view of the harmonic marker pulse problem.